In an elevator, generally, guide rails are arranged in pairs on an elevator shaft vertically. Being guided by these guide rails, an elevator car suspended by a main rope moves up and down the elevator shaft.
In order to allow the elevator car to be guided along the guide rails, a guide device is mounted on a car frame of the elevator car.
There are a roller-type guide device and a guideshoe-type guide device. Since these guide devices guide the elevator car with being in contact with the guide rails directly, these guide devices are predisposed to generate vibrations and noises due to distortion and connections of the guide rails, so such vibrations and noises are easily propagated into the elevator car though rollers and the like.
Thus, an elevator guiding apparatus that adopts a magnet unit for the guide rails is proposed (e.g. Japanese Patent Application Laid-open No. 2001-19286). In the elevator guiding apparatus, an attracting force of a magnet is generated between the opposing guide rails made of iron, guiding the elevator car in a non-contact manner, based on detection signals of a gap sensor.
FIG. 1 is a perspective view of the substantial part of the above-mentioned conventional elevator guiding apparatus. FIG. 2 is a plan view of a magnetic circuit of the magnet unit of FIG. 1.
As shown in FIGS. 1 and 2, the magnet unit 1 having an E-shaped configuration includes a center core 11, permanent magnets 12a, 12b connected to both sides of the center core 11 to have respective identical poles opposing to each other and electromagnets 13a, 13b connected to the permanent magnets 12a, 12b respectively to have respective identical poles opposing each other.
In FIG. 1, the magnet unit 1 is provided with a plurality of sensors 2 having gap sensors. The sensors 2 are adapted so as to detect the condition of a magnetic circuit (magnetic path) at gaps between the poles of the magnet unit 1 and a guide rail 3 in both of x, y directions (horizontal direction), in other words, detecting a physical quantity in the magnetic circuit.
As the elevator guiding apparatus controls attraction forces between the electromagnets 13a, 13b and the guide rail 3 in accordance with the exciting current control of the electromagnets 13a, 13b based on detection signals of the sensors 2, a not-shown elevator car equipped with the elevator guiding apparatus can move up and down in the elevator shaft while maintaining a non-contact condition between the apparatus and the guide rail 3.
In the elevator guiding apparatus using the above-constructed magnet unit, when the elevator car is in a normal position to the guide rail 3 and its operation is stable, it is possible to make exciting currents for coils 13aa, 13ba converge to zero, that is, so-called “zero power control” owing to the possession of the permanent magnets 12a, 12b. Accordingly, it is possible to suppress electric power consumption in the stationary state. Additionally, owing to the provision of the permanent magnets, an interval between the guide rail 3 and the magnet unit 1 could be broadened furthermore to allow the elevator car to elevate smoothly along the guide rail 3 with a long stroke and a low rigidity.
Note that, in the elevator guiding apparatus for guiding the movement of the elevator car along the guide rails 3, there are sensors 2 and magnet units 1 arranged at four (up, down, left and right) positions about the elevator car, facing the guide rails 3. In operation, with a calculation based on signals from the sensors 2 to detect the conditions of magnetic circuits at respective gaps between the guide rail 3 and the magnet unit 1 and signals from the magnet units 1 to detect exciting currents, a feedback control is applied on the exciting currents.
Regarding FIGS. 1 and 2, it is defined here that “x” represents a direction along which the magnet unit 1 opposes the guide rail 3 (generally, left-and-right direction of the elevator car viewed from its entrance side); “y” represents a direction perpendicular to the direction x in a horizontal plane (i.e. a depth direction of the elevator car); and “z” represents a vertical direction. In connection, “ξ”, “θ” and “φ” represents rotating directions around the directions x, y and z as axes of rotation.
Since the above-mentioned elevator guiding apparatus is constructed so as to control the magnet units 1 at four positions with a calculation based on respective signals from the upper and lower sensors 2 in the directions x and the upper and lower sensors 2 in the direction y to detect length of gaps and also based on respective values of exciting currents on detection, the elevator car is capable of moving up and down while being guided by the guide rails 3 under posture controls about “rolling direction” (i.e. the direction θ), “pitching direction” (i.e. the direction ξ) and “yawing direction” (i.e. the direction φ) as well as the translating movement in the directions x and y.
The magnet unit 1 shown in FIG. 2, however, has a problem described as follows.
For the description, firstly, left and right long surfaces in the section of the guide rail 3 are defined as a first guide face 3a and a second guide face 3b respectively, while a short surface of the section is defined as a third guide face 3c. Correspondingly, respective magnetic poles of the magnet unit 1 respectively opposing the guide faces 3a, 3b and 3c are defined as a first magnetic pole 1a, a second magnetic pole 1b and a third magnetic pole 1c, respectively. In FIG. 2, two-dotted lines with arrows denote magnetic flux lines by permanent magnets 12a, 12b. Consequently, it will be understood that magnetic flux (or flux density) at the third magnetic pole 1c becomes larger than magnetic flux (or flux density) at the first magnetic pole 1a or the second magnetic pole 1b since magnetic flux lines of the permanent magnets 12a, 12b are superimposed on each other at the third magnetic pole 1c. 
Additionally, it is noted that the shorter a magnetic path from a permanent magnet up to a magnetic pole gets, the smaller a leakage of flux from the permanent magnet becomes. Therefore, the flux density at the third magnetic pole 1c becomes larger than the flux density at the first magnetic pole 1a or the same at the second magnetic pole 1b because of a difference in respective magnetic paths between the permanent magnets 12a, 12b and the magnetic poles 1a, 1b, 1c. 
Consequently, an attraction force generated between the third guide face 3c and the third magnetic pole 1c is remarkably large in comparison with an attraction force between the first guide face 3a and the first magnetic pole 1a or between the second guide face 3b and the second magnetic pole 1b. 
The conventional magnet unit 1 mentioned above is generally used for an elevator guiding apparatus or a weighing apparatus for measuring a weight of an object in a non-contact manner. In the case of adopting the magnet unit 1 in the elevator guiding apparatus, however, the stability of an elevator car in its equilibrium situation is damaged due to the above difference of attraction force in between the backward-and-forward direction (i.e. the direction y) and the left-and-right direction (i.e. the direction x). Additionally, the magnets unit's reaction forces reactive to disturbance applied to the elevator car are different from each other depending on displacement directions of the elevator car.
The electromagnets 13a, 13b of the conventional magnet unit 1 have a great influence on the first magnetic pole 1a and the second magnetic pole 1b, respectively. While, the electromagnets 13a, 13b have little influence on the third magnetic pole 1c because of interposition of the permanent magnets 12a, 12b. 
In this way, the conventional magnet unit 1 has great differences in both attraction force and controllability between the directions (i.e. the direction x and the direction y) since the controllability of the electromagnets 13a, 13b against the third magnetic pole 1c is small while an attraction force of the permanent magnets 12a, 12b at the pole 1c is large. Accordingly, an elevator guiding apparatus adopting the above magnet unit(s) or the like has a reduced stability in operation since both responsibility and controllability of the magnets are different from each other depending on the directions.
In order to contemplate equalization in controllability with compensation for the reduced controllability of the electromagnets 13a, 13b to the third magnetic pole 1c, it might be supposed to supply the electromagnets 13a, 13b with great exciting currents in a moment of time. However, this measure is accompanied with great electric power consumption, requiring a capacious power source.